Development in DWDM (dense wavelength division multiplexing) transmission technology has remarkably increased the transmission capacity of an optical fiber, recently. In order to maintain required transmission quality in such high capacity transmission, not only a wavelength dispersion characteristic of an optical fiber but also influence by polarization mode dispersion (a phenomenon that a difference in group velocity occurs between two polarized waves vertically intersecting in a cross section of an optical fiber) cannot be neglected. One of causes of the polarization mode dispersion is that a core portion of an optical fiber, which is drawn from an optical fiber preform, is not a perfect circle. When the core portion is not a perfect circle, distribution of the refractive index in a cross section of the optical fiber does also not form a shape of a perfect concentric circle, so that the polarization mode dispersion would easily occur.
To solve such problem as polarization mode dispersion, it is proposed to add a twist to an optical fiber in a process for continuously manufacturing an optical fiber from an optical fiber preform. In this proposed method, an optical fiber drawn from an optical fiber preform is coated with a coating material (such as ultraviolet-cured type of resin, for example), and then, a twist is added to the optical fiber.
A device for continuously twisting an optical fiber, which is manufactured by adding a twist to an optical fiber, is disclosed, for example, as a roller swinging type of a twisting device in the U.S. Pat. Nos. 5,298,047, 5,418,881 or 6,076,376, or as an opposed roller type of a twisting device in the Japanese Patent Application (Publication No.: 2000-143277).
The present invention provides a device for continuously twisting an optical fiber and a system for manufacturing an optical fiber using the above device. In the device for continuously twisting an optical fiber according to the invention, an optical fiber drawn from an optical fiber preform is coated with a coating material, and then, a twist is added to the optical fiber. The device for continuously twisting an optical fiber according to the invention comprising:
a reciprocating roller, which rotates with its outer circumferential surface in contact with the running optical fiber while reciprocates along a center axis of rotation to continuously add a twist to the above optical fiber,
wherein the above outer circumferential surface of the reciprocating roller has a coefficient of friction xcexc for the optical fiber,
the coefficient of friction xcexc being lead from an operational formula of xcexc=(1/xcfx86)xc2x7ln(F/T), wherein xcfx86 is a contacting angle between the optical fiber and the reciprocating roller, F is maximum static friction of the optical fiber against the outer circumferential surface of the reciprocating roller, and T is tension of the optical fiber, and
the above coefficient of friction xcexc being set at a value in a range from not less than 0.6 to not more than 0.9.